The ability of an animal to alter behavior in response to changes in their environment is necessary for survival. Patients with neuropsychiatric disorders, especially addictive disorders, often have difficulty with this type of behavioral flexibility. One can measure the ability of an animal to alter goal-directed behavior following a change in outcome value using a reinforcer devaluation task. In this task, animals form associations between stimuli (e.g. cue) and specific reinforcer(s) (e.g. food rewards). The reinforcer is subsequently devalued by selective satiation (providing the food ad libitum). Following devaluation, normal subjects adjust their responding which reflects the new value of the reinforcer in the absence of new associative learning. The nucleus accumbens (NAc), in conconjuction with several other brain structures (e.g., orbitofrontal cortex and basolateral amygdala), is necessary for behavioral flexibly as measured by reinforcer devaluation tasks. However, it is unknown how DA input from the ventral tegmental area (VTA) to the NAc encodes goal-directed behavior following devaluation in real-time, or how manipulations of DA release can modulate this behavior. In order to assess this, two Specific Aims are proposed to address these issues. Aim 1 is designed to use electrochemical methods (fast scan cyclic voltammetry) to measure rapid DA signaling in the NAc core and shell to reward predictive cues and responses following reward devaluation. Aim 2 will use optogenetic manipulations to artificially stimulate DA release in NAc during acquisition or expression of the reinforcer devaluation task. Understanding the neural circuitry underlying flexible goal-directed behavior will help elucidate neural impairments in patients with neuropsychiatric disorders. As such, the proposed studies will provide critical insight into potentially new and more selective target systems for therapeutic intervention for individuals with maladaptive reward seeking, a hallmark of drug addiction.